The present invention relates generally to the use of certain block copolymers of ethylene oxide (EO) and propylene oxide (PO) as air-detraining agents that are stable in polymeric superplasticizers composed of comb polymers of alkylene oxide derivatives with acrylic acid derivatives.
The use of comb polymers of ethylene oxide/propylene oxide derivatives with derivatives of acrylic acid as superplasticizers for concrete compositions is well-known in the art as evidenced, for example, by prior-issued U.S. Pat. Nos. 6,139,623; 5,703,174; 5,670,578; 6,063,184; 5,798,425; 5,583,183 and 5,633,298 (the entire content of each such patent being expressly incorporated hereinto by reference).
The use of comb polymers of ethylene oxide/propylene oxide derivatives with derivatives of sulfonic acids as superplasticizers is also known in the art as evidenced by U.S. Pat. No. 5,614,017 (the entire content of which is expressly incorporated hereinto by reference). In this regard, the ""017 patent discloses the use of comb polymers of EO/PO with sulfonic acid derivatives as superplasticizer additives for cement compositions.
A typical example of a conventional comb polymer is one where the polymer has a monomeric unit comprised of carboxylic acid groups to which pendent groups comprising ethylene oxide and propylene oxide in various proportions are covalently attached. The use of such superplasticizers in cementitious compositions has several benefits such as, for example, significant reduction in the water content of the slurry, improved slump, high compressive strength, better freeze/thaw stability without causing significant retardation of the slurry.
The entrainment of air in concrete is known to be necessary to improve the freeze/thaw stability of concrete. However, air-entrainment in concrete needs to be carefully controlled. Air entraining agents such as rosins and anionic surfactants are commonly employed in concrete mixtures to control the size and the spacing of the air-bubbles formed in the concrete mix. Uneven spacing and/or excessively large size of the formed air-bubbles can lead to a loss of the concrete""s compressive strength. An excessive amount of air entrainment can also result in a significant loss in the compressive strength of the concrete mix.
One negative side-effect of the use of polymeric superplasticizers is that they entrain excessive air in the concrete slurry. The industry has therefore attempted to correct this deficiency by adding air-detraining agents to the concrete mix. Examples of air-detraining agents are typically hydrophobic materials such as nonionic surfactants with low HLB, silicone derivatives, di-butylphosphates, and alkyl phthalates. Since such air-detraining agents are hydrophobic and have very limited solubility in water, they cannot be incorporated into the polymeric superplasticizer solution. That is, an attempt to incorporate such conventional air-detraining agents results in phase separation as evidenced by the formation of a separate hazy layer usually on top of the polymeric superplasticizer solution. As a result of this insolubility, the industry has been forced to use separate tanks to store the superplasticizer solution and the air-detraining agent respectively and to only mix these separate components immediately prior to their incorporation in the cement slurry. As an alternative to separate storage, the superplasticizer solution and the air-detraining agent may be pre-mixed in a tank provided with continues stirring so as to prevent the phase separation of these two components, in which case surfactant stabilizers which function as an emulsifier for the air-detraining agent and the polymeric superplasticizer may be employed (see, the above-cited U.S. Pat. No. 6,139,623). Both of the approaches noted above are disadvantageous in that they are a source of inconvenience to the contractor and also result in additional costs to the operation. Further, the incompatibility of the superplasticizer and the air-detraining agent limits their utility in other areas of application.
Applicants have surprisingly found that certain air-detraining agents based on low molecular weight block polyethers comprising ethylene oxide (EO) and propylene oxide (PO), and being initiated with an initiator containing reactive diamine or glycol groups, have excellent stability in the polymeric superplasticizer solution. Typically, such block polyethers will have molecular weights in the range from about 700 to about 3500. (All molecular weights express herein are number average molecular weights.) Furthermore, the block polyethers will most preferably comprise ethylene oxide in a weight ratio of from about 10% to about 70% based on the molecular weight of the polyether.
It has also been found that, when the polymeric superplasticizer solution and the air-detraining agent are mixed in the desired ratios, the result is a crystal clear, isotropic solution that has the desired shelf life for the operation. Typically, the air detraining agent is present in an air detraining effective amount of less than about 1.0% by weight of the polymeric superplasticizer solution. More preferably, the air detraining agent will be present in an amount of between about 0.01 wt. % to about 1 wt. %, and most preferably between about 0.1 wt. % to about 0.7 wt. %, based on the weight of the polymeric superplasticizer solution. An especially preferred amount of the air detraining agent is from about 0.1 wt. % to about 0.5 wt. %, based on the weight of the polymeric superplasticizer solution.
In one embodiment, therefore, the current invention comprises a polymeric superplasticizer and an air-detraining effective amount of an air detraining agent. Preferably, the polymeric superplasticizer is a comb polymer comprised of polycarboxylic acid or partial esters to which are attached pendent groups consisting essentially of polyoxyalkylene groups. The term xe2x80x9cpolyoxyalkylenexe2x80x9d refers to a mixture of polyoxyalkylene groups such as polyethylene oxide, polypropylene oxide and polybutylene oxide. The comb polymer employed as a polymeric superplasticizer in accordance with the current invention can be represented by the following general formula (I): 
where R1=H or CH3;
R2=COOM, OCH3, SO3M, Oxe2x80x94COxe2x80x94CH3, COxe2x80x94NH2, preferably COOM,
where M is a salt of Na, Ca, K, or Mg;
R3=is an alkylene oxide group selected from the group consisting of ethylene oxide, propylene oxide and/or butylene oxide, and wherein the alkylene oxide groups can be in either a block or random distribution;
R4=CH3or alkyl;
Q=C(O)O, C(O)NH, CH2O, CH2N, O;
m and n are such that between 98% to 2 % of m units and between about 2% to about 98% of n units are present in the polymer; and
p is between 1 to 300. A particularly preferred polymeric superplasticizer is SOKALAN(copyright) HP 80 commercially available from BASF Corporation.
In another embodiment according to the present invention, the block polyether is a block copolymer of ethylene oxide and propylene oxide represented by the following general formula (II):
xe2x80x83[R3R2]n(R1)n
where R1 is an initiator containing reactive terminal groups capable of adding to C2-C4 epoxides, such as ethylene oxide, propylene oxide and butylene oxide; R2 is either propylene oxide or butylene oxide; R3 is ethylene oxide, and n represents the functionality of the initiator and is a number greater than or equal to 2, and wherein R3 and R2 are interchangeable in the formula. Most preferably, ethylene oxide is employed, with up to about 30% of propylene oxide. Most preferably, the initiator R1 is an alkylene diamine or glycol, such as etheylene diamine or propylene glycol.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.